Nanomachining, by definition, involves mechanically removing nanometer-scaled volumes of material from, for example, a photolithography mask, a semiconductor substrate/wafer, or some other monolith. For the purposes of this discussion, “substrate” will refer to any object upon which nanomachining may be performed.
Typically, nanomachining is performed by applying forces to a surface of a substrate with a tip (e.g., a diamond cutting bit) that is positioned on a cantilever arm of an atomic force microscope (AFM). More specifically, the tip is typically first inserted into the surface of the substrate. Then, the tip is dragged through the substrate in a plane that is parallel to the surface (i.e., the xy-plane). This results in displacement and/or removal of material from the substrate as the tip is dragged along.
As a result of this nanomachining, debris is generated on the substrate. More specifically, small particles may form during the nanomachining process as material is removed. These particles, in some instances, remain on the substrate once the nanomachining process is over. Such particles are often found, for example, in trenches and/or cavities present on the substrate.
In order to remove such debris, particularly in high-aspect photolithography mask structures and electronic circuitry, wet cleaning techniques are often used. More specifically, the use of chemicals in a liquid state and/or agitation of the overall mask or circuitry is typically employed. However, both chemical methods and agitation methods such as, for example, megasonic agitation, can destroy both high-aspect ratio structures and mask optical proximity correction features (i.e., features that are generally so small that these features do not image, but rather form diffraction patterns that are used beneficially by mask designers to form patterns).
In order to better understand why high-aspect shapes and structures are particularly susceptible to being destroyed by chemicals and agitation, one has to recall that such shapes and structures, by definition, include large amounts of surface area and are therefore very thermodynamically unstable. As such, these shapes and structures are highly susceptible to delamination and/or other forms of destruction when chemical and/or mechanical energy is applied.
In view of the above, other currently available methods for removing debris from a substrate make use of cryogenic cleaning systems and techniques. When employing such systems and techniques, the substrate containing the high aspect shapes and/or structures is effectively “sandblasted” using carbon dioxide particles instead of sand.
Unfortunately, even cryogenic cleaning systems and processes are also known to destroy high aspect features. In addition, cryogenic cleaning processes affect a relatively large area of a substrate (e.g., areas that may be approximately 10 millimeters across or more). Naturally, this means that areas of the substrate that may not need to have debris removed therefrom are nonetheless exposed to the cleaning process and to the potential structure-destroying energies associated therewith.